Objectives: A) The regulation of sodium excretion by the kidney with respect to natriuretic substances of pituitary origin, angiotensin and adaptive changes in experimental renal disease. B) The regulation of calcium metabolism at the cellular level using the canine erythrocyte as a model system and the influence of parathyroid hormone on calcium and sodium handling by the renal tubule. C) The regulation of acid excretion by the kidney in terms of the influence of parathyroid hormone on the proximal tubular reabsorption of bicarbonate and the patho- physiology of acid excretion in certain diseases by examining the influence of sulfate and phosphate on urinary acidification.